Fastening Element

ABSTRACT

A fastening element is provided, which is adapted to cooperate with a tie member to exert a compressive force on first and second components, the fastening element comprising an inner portion ( 50 ) resiliently joined to an outer portion ( 52 ), such that when a tensile reaction force is applied to the tie member as a result of the compressive force, the reaction force causes the outer portion ( 52 ) to be displaced relative to the inner portion ( 50 ). The fastening element may further comprise a washer ( 56 ) rotatably attached to the outer portion ( 52 ) by a cage ( 54 ). An indicator element for use with such a fastening element is also provided, together with a method of securing a first component to a second component by means of such a fastening element.

FIELD OF THE INVENTION

[0001] This invention relates to a fastening element for use with a tiemember to fasten a first component to a second component, to anindicator element for use with such a fastening element to indicatefastness of said components, and to a method of securing a firstcomponent to a second component using such an element and a tie member.

BACKGROUND OF THE INVENTION

[0002] It is well known to fasten two or more components together bypassing a bolt through the components and tightening a nut onto thebolt, so that the bolt head and nut each exert a clamping force on thecomponents.

[0003] Vibration and flexure of the components tend to loosen the nut onthe bolt, and such loosening is prevented only by friction between thebolt head and nut and the components.

[0004] Where the components are relatively compliant, the nut may haveto be loosened by up to three turns before all of the clamping force onthe components is lost. Where, on the other hand, the components arerelatively stiff, the nut may have to be loosened by as little as oneninth of a turn before all of the clamping force is lost. The loss ofthe clamping force substantially reduces the friction between the bolthead and nut and the components, allowing the nut to move freelyrelative to the bolt until the components eventually separate.

[0005] It is known to interpose a split or spring washer between the nutand the component, the washer being compressed by the clamping forceexerted on the components and expanding against the component and nut inthe event of a momentary reduction of the clamping force, for exampledue to flexure of the components, so as to prevent the nut fromloosening. However, the use of split or spring washers is notparticularly effective and introduces an undesirable complication intoan assembly line.

[0006] A particular combination of components, nut and bolt will have anoptimum clamping force, which gives a high degree of friction betweenthe bolt head, nut and components, but avoids excessive distortion ofthe components, snapping the bolt or stripping the threads of the boltor nut.

[0007] Once the optimum clamping force has been determined, taking intoaccount thread pitch, bolt diameter, loaded bolt length, and lubricity,surface finish and dimensional variation of the components, the clampingforce is obtained by applying a predetermined torque to the nut.

[0008] At present, the only method of determining whether a nut has beencorrectly tightened is by means of a torque spanner. However, if the nuthas been correctly tightened, the application of the torque spanner tothe nut will cause the nut to be further tightened, and the optimumclamping force to be exceeded.

SUMMARY OF THE INVENTION

[0009] According to a first aspect of the invention there is provided afastening element for use with a tie member to fasten a first componentto a second component, the fastening element being adapted forattachment to the tie member, which in use passes through a part of atleast one of the components, and for cooperating with the tie member toexert a compressive force on the components, characterised in that theelement comprises an inner portion resiliently joined to an outerportion, in such a way that, when a tensile reaction force is applied tothe tie member as a result of said compressive force, said force causesthe outer portion to be displaced relative to the inner portion.

[0010] The invention therefore provides a fastening element for use witha tie member, which element enables the magnitude of a tensile forceapplied to the tie member to be determined without altering themagnitude of the force, and which is operable to prevent relativemovement of the fastening element and the tie member in the event of amomentary reduction of the compressive force on the components.

[0011] Preferably the inner portion is formed integrally with the outerportion.

[0012] Preferably the relative position of the inner and outer portionsis such that the displacement of the outer portion relative to the innerportion is an axial displacement.

[0013] The fastening element may be attached to the tie member by anyconvenient means, for example crimping onto, or welding to, the member,or may be integrally formed with the tie member. Preferably, however,the inner portion is tapped so as to be engageable with a threadedportion at a first end of the member.

[0014] Said compressive force may be exerted by means of a nut tightenedagainst the second component onto a threaded portion at a second end ofthe member, but preferably the outer portion of the element is formedwith flats for engagement with a spanner or like tool, such that thecompressive force and hence the tensile reaction force may be applied bymeans of tightening the element, against the first component, onto thethreaded portion at the first end of the member. In this case the secondend of the member may be formed with a head for engagement with thesecond component, or be fastened to the second component, for example bywelding, or the member may be integrally formed with the secondcomponent.

[0015] The fastening element may advantageously be formed from sheet orstrip spring steel.

[0016] Preferably, the fastening element comprises a nut, for use with atie member in the form of a bolt or stud.

[0017] The fastening element may advantageously further comprise awasher that is rotatably attached to the nut, and that, in use, isinterposed between the nut and the components.

[0018] Preferably the washer is annular, such that in use, the tiemember passes through the washer.

[0019] The fastening element may advantageously further comprise cagemeans having first and second pluralities of axial, radially inwardlyprojecting claws, the first plurality of claws being engageable with thenut and the second plurality of claws being engageable with the washer.

[0020] In a preferred embodiment of the fastening element the nut isformed with a generally frusto-conical portion and the annular washer isformed with a continuous groove in its external circumference, and thefirst plurality of claws of the cage are engageable with thefrusto-conical portion of the nut and the second plurality of claws areengageable with the groove of the washer.

[0021] Preferably the washer is formed from hardened steel and the cageis formed from mild or spring steel.

[0022] In this way during tightening of a tapped fastening element ontoa threaded tie member against a component, the nut rotates against thewasher rather than against the component, and there is little, if any,relative movement between the washer and the component, such thatscoring of the surface of the component is much reduced.

[0023] According to a second aspect of the invention there is providedan indicator element for use with a fastening element in accordance withthe first aspect of the invention, the indicator element beingreleasably engageable with a fastening element such that the indicatorelement is retained by the fastening element when the outer portion ofthe fastening element is displaced relative to the inner portion, andreleased if the displacement of the outer portion relative to the innerportion decreases substantially.

[0024] The second aspect of the invention therefore provides anindicator element that may be engaged with a fastening element inaccordance with the first aspect of the invention, once the fasteningelement is exerting a desired compressive force on a component, butwhich will be released from the fastening element if the compressiveforce decreases by a substantial amount, for example due to loosening ofthe fastening element, and hence provides a visual indication of thedecrease in the compressive force.

[0025] Moreover, the indicator element enables a very quick check to becarried out of whether a fastening element is exerting a desiredcompressive force on a component, simply by attempting to engage theindicator element with the fastening element, since the indicatorelement will be retained only if the fastening element is exerting thedesired compressive force.

[0026] The indicator element may advantageously be adapted to beengageable with an internal surface of the outer portion of thefastening element when the outer portion is displaced relative to theinner portion.

[0027] In a preferred embodiment the indicator element comprises a capfor placing over the fastening element, the cap having a centralinternal tubular member with a perpendicularly outwardly projecting lipthat is engageable with an internal surface of the outer portion of thefastening element when the outer portion is displaced relative to theinner portion. When the outer portion is not displaced relative to theinner portion, the external surface of the inner portion occludes theinternal surface of the outer portion, such that the lip of the tubularmember cannot engage with the internal surface of the outer portion.

[0028] The indicator element may advantageously be formed from aplastics material.

[0029] Preferably the indicator element is formed from nylon-66.

[0030] According to a third aspect of the invention there is provided amethod of securing a first component to a second component, by means ofa fastener comprising an element as hereinabove described and a tiemember, the method comprising the steps of applying a progressivelyincreasing compressive force to the two components, by means of thefastener, and determining whether said displacement of the inner portionrelative to the outer portion reaches a minimum magnitude indicative ofthe soundness of the attachment of the two components.

[0031] The step of determining whether the displacement reaches aminimum magnitude may advantageously be by measurement of thedisplacement of the inner portion relative to the outer portion.

[0032] Preferably the step of determining whether the displacementreaches a minimum magnitude is by visual inspection of the displacementof the inner portion relative to the outer portion.

[0033] Alternatively, the step of determining whether the displacementreaches a minimum magnitude may advantageously be by attempting toengage an indicator element as hereinbefore described with the fasteningelement, and observing whether the indicator element is retained by thefastening element.

[0034] The method may advantageously further comprise the step ofdetermining whether the displacement of the inner portion relative tothe outer portion is less than a maximum magnitude, corresponding to amaximum desired magnitude of compressive force.

[0035] Preferably the inner portion of the fastening element is tappedand a first end of the tie member has a threaded portion, the step ofapplying the compressive force being achieved by screwing the tappedinner portion of the element onto the threaded portion of the member.

[0036] Preferably the outer portion of the fastening element is formedwith flats for engagement with a spanner or like tool, and the step ofapplying said force is achieved by applying a torque to the fasteningelement.

[0037] The invention also lies in a nut comprising a fastening elementas hereinabove described and a bolt for use therewith.

[0038] The invention will now be described by way of illustrativeexample and with reference to the accompanying drawings, in which:

[0039]FIG. 1 is a perspective view of a first nut in accordance with thefirst aspect of the invention;

[0040]FIG. 2 is a sectional view of the first nut;

[0041]FIG. 3 is a representation of the manufacturing process of thefirst nut;

[0042]FIG. 4 is an exploded view of a tool used in the manufacturingprocess;

[0043]FIG. 5 is a perspective view of a second nut;

[0044]FIG. 6 is a sectional view of the second nut;

[0045]FIG. 7 is a sectional view of the second nut when tightened onto astud;

[0046]FIG. 8 is a sectional view of an indicator cap in accordance withthe second aspect of the invention; and

[0047]FIG. 9 is a sectional view of the second nut when tightened ontothe stud and fitted with the indicator cap.

DETAILED DESCRIPTION OF AN EMBODIMENTS

[0048] The first nut of FIG. 1 consists of an inner portion 10 and anouter portion 12, the inner and outer portions being integrally formedas a single component from spring steel.

[0049] Turning to FIG. 2, the inner portion 10 is generally tubular,having a cylindrical neck 14 and a frusto-conical skirt 16. The internalsurface of the neck is tapped for engagement with the threads of a boltor stud (not shown). The external surface of the neck 14 is cylindrical.The end surface 18 of the neck 14 is planar. The internal and externalsurfaces of the skirt 16 are frusto-conical and the end surface of theskirt forms a first part of the base 20 of the nut.

[0050] The outer portion 12 is also generally tubular, having ahexagonal neck 22 and a generally frusto-conical skirt 24. The internaland external surfaces of the neck 22 are hexagonal, the six flats of theexternal surface, one of which, 26, is visible in FIG. 2, being adaptedto enable the nut to be tightened onto the bolt or stud by, for example,a torque spanner. The end surface 28 of the neck 22 is also planar. Theinternal and external surfaces of the skirt 24 are generallyfrusto-conical, and the end surface of the skirt forms a second part ofthe base 20 of the nut.

[0051] The nut is complicate in structure, such that the skirt 16 of theinner portion 10 is joined at the base 20 of the nut to the skirt 24 ofthe outer portion 12, the external surface of the skirt 16 is in contactwith the internal surface of the skirt 24, and the cylindrical externalsurface of the neck 14 is in contact with the hexagonal internal surfaceof the neck 22 at the midpoint of each of its sides. When the nut is notstressed, the end surfaces of the inner and outer portions, 18 and 28respectively, are coplanar.

[0052] In use, the nut is tightened onto a bolt that passes through partof a component, until the base 20 of the nut engages with the component.As the nut is tightened further onto the bolt against the component, theforce exerted by the threads of the bolt on the tapped internal surfaceof the inner portion causes the end surface 18 of the inner portion tomove downwards relative to the end surface 28 of the outer portion, asthe skirt 16 of the inner portion, partially collapses. As this happens,the radius of the base of the nut remains unchanged, the skirt 16 thuscollapsing in a similar fashion to a rubber plunger for unblockingdomestic waste water pipes. The relative displacement of the endsurfaces 18 and 28 is proportional to the tensile reaction force exertedon the bolt (as a result of the compressive force exerted by the nut andbolt on the components being fastened together), and therefore providesan indication, measurable with a micrometer, for example, if notdiscernible by the naked eye, of whether the nut has been correctlytightened.

[0053] Turning next to FIG. 3, the nut is formed from a sheet of springsteel. Stages 1 to 12 show a deep drawing operation in which the neckand skirt of the inner portion of the nut are formed and a central holeis punched in the end surface of the neck, leaving a circular flangeprojecting radially from the base of the skirt.

[0054] Stages 13 to 15 show a redrawing operation in which a cupped dieencloses the neck and skirt of the inner portion of the nut and bears onthe circular flange. The cupped die drives the inner portion of the nutinto a funneled die, thereby bending the circular flange upwards so asto surround the inner portion of the nut.

[0055] Stages 16 and 17 show a simulated cam tool operation, in whichthe hexagonal form is imparted to the outer portion of the nut. Thesimulated cam tool is shown in FIG. 4, and comprises a die block 30,base 32, mandril 34 and split collet 36. The split collet 36 is made upof three identical segments 38, 40 and 42.

[0056] The die block 30 is hollow, the internal surface having an upper,tapered portion 44 and a lower, parallel-sided portion 46. The lower,parallel-sided portion 46 is sized to receive the base 32, which has acentral, parallel-sided hole sized to receive the mandril 34. The tip ofthe mandril fits inside the inner portion of a nut 48, which ispartially visible in the split collet 36. The split collet fits aroundthe nut. In FIG. 4 the three segments 38, 40 and 42 of the split colletare shown enclosing the nut 48,and in contact with one another. Inpractice this would not be possible until the simulated cam tooloperation had been completed.

[0057] The external surface of the split collet is tapered, and sizedsuch that with a nut placed between the three segments of the collet,the narrow end of the collet just fits into the upper, wide part of theinternal taper of the die block. The internal surface of the splitcollet is hexagonal and the simulated cam tool operation consists offorcing the split collet containing the nut into the die block in whichthe base and mandril are held. The tapered portion 44 of the die blockforces the three segments of the split collet inwards, thereby formingthe hexagonal external surface of the outer portion. The base serves tocentre the mandril relative to the die block and split collet, and themandril ensures that the forces are applied symmetrically around the nutby the split collet.

[0058] Returning to FIG. 3, stage 18 shows a roll form tappingoperation, in which an internal thread is formed on the internal surfaceof the inner portion of the nut.

[0059] The second nut of FIG. 5 consists of an inner portion 50, anouter portion 52, a cage 54 attached to the outer portion 52 and to awasher 56. The inner and outer portions are integrally formed as asingle component from spring steel, the cage is formed from spring steeland the washer is made of hardened steel.

[0060] Turning to FIG. 6, the inner and outer portions of the second nutare substantially as described in relation to the first nut. However,the end surface of the neck of the inner portion is convex rather thanplanar, and the external surface of the skirt and neck of the innerportion, and the internal surface of the skirt and neck of the outerportion define an annular cavity inside the nut. When the nut is notstressed the apex of the convex end surface of the neck of the innerportion and the end surface of the neck of the outer portion arecoplanar.

[0061] Returning to FIG. 5, the cage 54 consists of a hoop 58 formedwith long, radially inwardly directed claws 60 that project axially fromone edge of the hoop, and short, radially inwardly directed claws 62that project axially from the other edge of the hoop. The hoop is formedwith nine long claws and nine short claws, which are disposedequidistantly around the edges of the hoop. In FIG. 5 six long claws andthree short claws are visible.

[0062] The washer 56 is annular and formed with a continuous groove 64in its external circumferential surface.

[0063] The short claws of the cage are engageable with the groove in thewasher, and the long claws are engageable with the external surface ofthe skirt of the outer portion. With the long claws engaged with theskirt of the outer portion and the short claws engaged with the groovein the washer, the washer is retained adjacent to the base of the skirt,but capable of rotational movement relative to the inner and outerportions of the nut.

[0064] In this way, when the nut is tightened onto a stud 66 against acomponent 68, as shown in FIG. 7, the washer 56 may remain stationaryrelative to the component, and the inner and outer portions be rotatedrelative to the washer and the component, so as to avoid the scoring ofthe surface of the component which would occur without the presence ofthe washer.

[0065] When the nut is tightened onto the stud 66 there is a relativeaxial displacement of the inner and outer portions of the nut, in whichthe inner portion is displaced towards the washer relative to the outerportion, such that the apex of the end surface of the inner portion iscloser to the washer than the end surface of the outer portion.

[0066]FIG. 8 shows an indicator cap that is formed from nylon-66. Thecap is generally cup-shaped, having a hexagonal, parallel-sided closedend 70, and a flared circular open end 72. A central hexagonal, tubularmember 74 projects from the closed end of the cap towards the open endof the cap. The end of the tubular member nearer to the open end of thecap is formed with a lip 76 that projects perpendicularly from thetubular member.

[0067] The internal dimensions of the cap are such that, but for thepresence of the tubular member, the cap would form a snug fit over thesecond nut.

[0068] The external measurements of the lip of the tubular member areslightly larger than the internal measurements of the hexagonal neck ofthe outer portion of the second nut. The internal measurements of thetubular member are slightly smaller than the external diameter of theneck of the inner portion of the second nut.

[0069] Thus when the second nut is tightened onto a stud, as shown inFIG. 7, such that the inner portion is displaced towards the washerrelative to the outer portion, the cap may be placed over the nut andthe lip of the tubular member will deform slightly so as to engage withthe internal surface of the neck of the outer portion of the nut.

[0070] This is shown in FIG. 9. The cap is held in place by frictionbetween the deformed lip of the cap and the internal surface of the neckof the outer portion of the nut, since the tubular member is slightlywider than the internal measurements of the neck of the outer portion.

[0071] If the nut subsequently loosens, the inner portion of the nutwill move away from the washer relative to the outer portion, until theapex of the end surface of the neck of the inner portion and the endsurface of the neck of the outer portion are coplanar. The externaldiameter of the neck of the inner portion is slightly greater than theinternal measurements of the tubular member of the cap, such that as theend surface of the neck of the inner portion moves away from the washer,it engages with the tubular member and pushes the cap off the nut, thusproviding a visual indication that the nut has loosened.

[0072] It will be apparent that the above description relates only totwo embodiments of the invention, and that the invention encompassesother embodiments as defined by the foregoing statements of theinvention.

1. A fastening element for use with a tie member to fasten a firstcomponent to a second component, the fastening element being adapted forattachment to the tie member, which in use passes through a part of atleast one of the components, and for cooperating with a tie member toexert a compressive force on the components, characterised in that theelement comprises an inner portion resiliently joined to an outerportion, in such a way that, when a tensile reaction force is applied tothe tie member as a result of said compressive force, said force causesthe outer portion to be displaced relative to the inner portion.
 2. Afastening element according to claim 1, wherein the inner portion isformed integrally with the outer portion.
 3. A fastening elementaccording to claim 1, wherein the inner and outer portions are sopositioned relative to one another that the displacement of the outerportion relative to the inner portion is an axial displacement.
 4. Afastening element according to claim 1, wherein the inner portion istapped so as to be engageable with a threaded portion at a first end ofthe tie member.
 5. A fastening element according to claim 1, wherein theouter portion is formed with flats for engagement with a spanner or liketool.
 6. A fastening element according to claim 1, wherein the fasteningelement is formed from sheet or strip spring steel.
 7. A fasteningelement according to claim 1, wherein the fastening element comprises anut, for use with a tie member in the form of a bolt or stud.
 8. Afastening element according to claim 7, wherein the fastening elementfurther comprises a washer that is rotatably attached to the nut, andthat, in use, is interposed between the nut and the components.
 9. Afastening element according to claim 8, wherein the washer is annular,such that in use, the tie member passes through the washer.
 10. Afastening element according to claim 9, wherein the fastening elementfurther comprises cage means having first and second pluralities ofaxial, radially inwardly projecting claws, the first plurality of clawsbeing engageable with the nut and the second plurality of claws beingengageable with the washer.
 11. A fastening element according to claim10, wherein the nut is formed with a generally frusto-conical portionand the annular washer is formed with a continuous groove in itsexternal circumference, and the first plurality of claws of the cagemeans are engageable with the frusto-conical portion of the nut and thesecond plurality of claws are engageable with the groove of the washer.12. A fastening element according to claim 8, wherein the washer isformed from hardened steel.
 13. A fastening element according to claim10, wherein the cage means is formed from mild or spring steel.
 14. Anindicator element for use with a fastening element, the indicatorelement being releasably engageable with a fastening element accordingto claim 1 such that the indicator element is retained by the fasteningelement when the outer portion of the fastening element is displacedrelative to the inner portion, and released if the displacement of theouter portion relative to the inner portion decreases substantially. 15.An indicator element according to claim 14, wherein the indicatorelement is adapted to be engageable with an internal surface of theouter portion of the fastening element when the outer portion isdisplaced relative to the inner portion.
 16. An indicator elementaccording to claim 14, wherein the indicator element comprises a cap forplacing over the fastening element, the cap having a central internaltubular member with a perpendicularly outwardly projecting lip that isengageable with an internal surface of the outer portion of thefastening element when the outer portion is displaced relative to theinner portion.
 17. An indicator element according to claim 14, whereinthe indicator element is formed from a plastics material.
 18. Anindicator element according to claim 17, wherein the indicator elementis formed from nylon-66.
 19. A method of securing a first component to asecond component, by means of a fastener comprising a fastening elementaccording to claim 1, and a tie member, the method comprising the stepsof applying a progressively increasing compressive force to the twocomponents, by means of the fastener, and determining whether adisplacement of the inner portion relative to the outer portion reachesa minimum magnitude indicative of the soundness of the attachment of thetwo components.
 20. A method according to claim 19, wherein the step ofdetermining whether the displacement reaches a minimum magnitude is bymeasurement of the displacement of the inner portion relative to theouter portion.
 21. A method according to claim 19, wherein the step ofdetermining whether the displacement reaches a minimum magnitude is byvisual inspection of the displacement of the inner portion relative tothe outer portion.
 22. A method according to claim 19, wherein the stepof determining whether the displacement reaches a minimum magnitude byattempting to engage an indicator element according to claim 14 with thefastening element, and observing whether the indicator element isretained by the fastening element.
 23. A method according to claim 19,wherein the method further comprises the step of determining whether thedisplacement of the inner portion relative to the outer portion is lessthan a maximum magnitude, corresponding to a maximum desired magnitudeof compressive force.
 24. A method according to claim 19, wherein theinner portion of the fastening element is tapped and a first end of thetie member has a threaded portion, the step of applying the compressiveforce being achieved by screwing the tapped inner portion of the elementonto the threaded portion of the member.
 25. A method according to claim19, wherein the outer portion of the fastening element is formed withflats for engagement with a spanner or like tool, and the step ofapplying said force is achieved by applying a torque to the fasteningelement.
 26. A fastening element according to claim 1, and a bolt foruse therewith.